A number of brake systems have been proposed in the past that use an air supply controlled through a foot valve and/or hand valve which delivers air to the tractor-trailer unit in either an in-line system or a sequential system. The system that has been most successful in the past has been a combination foot and hand valve which allows the operator to individually control the trailer brakes independent of the tractor brakes on demand, however, the system requires the coordination of hand and foot of the operator and a more desirable arrangement has been sought which leaves no decision to the operator but which automatially delivers air to the trailer ahead of the tractor.
Another problem involved is the various load requirements of the trailer which can vary from empty to maximum and changes the braking characteristics of the trailer. This problem has been addressed by numerous patents and is commonly referred to and partially solved by the use of "load-controlled" or "load-sensing" valves such as Pat. No. 4,418,965 or Pat. No. 4,324,436.
Yet another problem to be addressed is the amount of air delivered to the tractor in relation to the amount of air delivered to the trailer which can be controlled at all levels of air-pressure and the manner in which the air-pressure is delivered automatically under all circumstances.
Still another problem exists due to the different distances involved of the tractor and trailer from the source of air supply via the foot or hand valve. If the tractor and trailer is "in-line", the air is delivered first to the tractor and then to the trailer which can cause serious problems. This problem is addressed by various devices such as Pat. No. 3,747,992 which electro-pneumatic system and has to due primarily with response time.
Another important problem with conventional systems is the use of the "jake brake" which only breaks the tractor and can cause under certain conditions, jack-knifing, skidding of the trailer, etc.
These and other problems are addressed by the present invention which eliminates many components and provides additional advantages not heretofore available.